1. Field of the Invention
The present invention relates to a photographic apparatus that captures object light and generates an image signal, and a lens barrel that houses a picture-taking optical system and can be extended and collapsed.
2. Description of the Related Art
In recent years, in addition to conventional cameras that use silver films for taking pictures, digital cameras that use a solid-state image pickup device, such as a CCD image pickup device or MOS image pickup device, have rapidly become widespread. The digital cameras form an object image on the solid-state image pickup device and generate an image signal.
The digital cameras, which are also required to have high portability as well as high picture-taking performance, are designed to house the collapsed lens barrel including the taking lens in the body so that the focal length can be changed, picture-taking can be achieved at a desired angle of view, and high portability can be assured.
Commonly-used taking lenses having a variable focal length are composed of three or more lens groups. In particular, widely used is a taking lens in which the lens group disposed at the rear end thereof along the optical axis serves as a focusing lens, and the focusing lens is displaced along the optical axis to achieve focus adjustment. Typically, a member that controls the quantity of light, such as a shutter or diaphragm, is additionally provided between the front lens group and the rear lens group or between the rear lens group and the focusing lens. As techniques relating to the present invention described later, there have been known shutters using an electrooptic element, such as a liquid crystal shutter using a liquid crystal (see patent references 1 and 2) and a PLZT shutter using a polarizing plate (see patent reference 3).
Such a camera that houses the collapsed lens barrel in the body has been made thinner by reducing the spaces between the lens groups or between the lens groups and the shutter are reduced to a minimum when the lens barrel is collapsed. However, this approach can make the digital camera thinner only to a limited extent.
There has been proposed an approach to vary the focal length in which the rear lens group is disposed on the optical axis in the telephoto mode and the rear lens group is displaced from the optical axis in the wide-angle mode (see the patent reference 4). However, this approach is intended only for varying the focal length and doesn't contribute to reducing the thickness of the camera.
Furthermore, compared to cameras which cannot change the length of the lens barrel, cameras of this type tend to introduce dust into the lens barrel, and the dust in the lens barrel may adhere to the taking lens to cause degradation of image quality.
To address this problem, there have been proposed techniques for cleaning the front surface of the taking lens provided on the front of the camera (see the patent references 5, 6 and 7). However, there have not been proposed measures against the dust in the lens barrel which adheres to the taking lens and causes degradation of image quality.
In addition, the patent reference 8 discloses a camera which has a lens barrel that incorporates a taking lens composed of plural lens groups and can be extended or collapsed and is reduced in thickness in the collapsed state by retracting, from the optical axis of the taking lens, the second lens group along the optical axis of the taking lens or both the first and second lens groups from the front along the optical axis.
However, the patent reference 8 doesn't propose any measure against the dust in the lens barrel which adheres to the taking lens and causes degradation of image quality.
Patent Document 1: Japanese Patent Laid-Open No. 9-163240
Patent Document 2: Japanese Patent Laid-Open No. 2001-61165
Patent Document 3: Japanese Patent Laid-Open No. 8-304875
Patent Document 4: Japanese Patent Laid-Open No. 5-34769 Patent Document 5: Japanese Patent Laid-Open No. 9-200591
Patent Document 6: Japanese Patent Laid-Open No. 7-64152
Patent Document 7: Japanese Patent Laid-Open No. 5-344396
Patent Document 8: Japanese Patent Laid-Open No. 2003-315861